This invention pertains generally to internal combustion engine control systems, and more specifically to engine valvetrain mechanisms and cooling systems.
Internal combustion engines, including compression ignition engines and spark ignition engines regularly undergo redesign efforts to improve efficiency and enhance fuel economy. Compression-ignition engines and direct-injection spark-ignition engines are gaining in popularity due in part to improved fuel economy, which may exceed 20% improvement compared to a similarly-sized, conventional spark-ignition engine. Compression-ignition engines and direct-injection spark-ignition engines operate with excess air in the combustion process, which is also referred to as operating lean of stoichiometry. An engine that operates lean of stoichiometry does so without a throttle valve in the air intake manifold. Stoichiometry is an air/fuel ratio at which there is a sufficient amount of oxygen from the air mixed with the fuel to completely oxidize the fuel during combustion. When air freely flows into the cylinders on an intake stroke of a combustion cycle, less pumping energy is required, leading to a fuel economy benefit. Engines that operate lean of stoichiometry are classified as heavy-duty diesel, light-duty diesel, and direct-injection gasoline engines.
The induction of excess air helps improve engine efficiency and vehicle fuel economy, but also reduces the quantity of heat energy that is created and transferred from a combustion chamber to the engine block and engine cooling system during combustion. When there is less amount of heat generated by the engine, there is less heat transferred to the engine cooling system. In addition, the excess air cools the engine, especially during low speed, low power operation. The engine cooling system uses a heat exchanger to transfer heat from the engine to the passenger compartment of the vehicle. The cooling system is designed to handle engine heat rejection from combustion that is created when the engine is operating at high speed, high power conditions in high ambient temperatures. A typical dynamic operating range for a compression-ignition engine is from 0 kW to 225 kW for a 6.6 liter engine. A cooling system that is designed to remove rejected heat from the engine when it is operating at 225 kW will be over-designed for a more typical operation of 30 kW, such as when the vehicle is operating at a steady-state cruise. Operation of the engine at a more typical operating point near 30 kW may not provide sufficient heat rejection by the engine to the cooling system. In addition, the capacity of the cooling system affects the amount of time required to warm the engine and passenger compartment. This is based upon fundamental heat transfer characteristics of the system and the thermal capacity of the cooling system. When a request for heat in the passenger compartment is not met by heat transfer from the engine in a reasonable amount of time, a vehicle""s occupants experience discomfort. The amount of time necessary to adequately defrost windows and windshields also increases, particularly with compression-ignition engines and direct-injection gasoline-fueled engines. Hence there is an ongoing concern to be able to rapidly transfer heat from the engine to the passenger compartment of a vehicle to provide for passenger comfort and visibility.
Manufacturers of spark ignition engines generally implement a cylinder deactivation system to broaden the dynamic operating range of a specific engine configuration, thus leading to improvements in engine efficiency and vehicle fuel economy. Cylinder deactivation is currently being implemented on throttled spark-ignition engines such as are commonly used in cars and light-duty trucks. These engines obtain a relatively large fuel economy benefit (8% to 25%) from use of cylinder deactivation when operating at low engine operating points. This benefit is primarily a result of reduced engine pumping losses during operation of the cylinder deactivation system. Cylinder deactivation is currently not used on compression-ignition or direct-injection spark-ignition engines. There is little efficiency gain or fuel economy benefit for these engine configurations because they operate in an unthrottled mode with excess air. Therefore compression ignition or direct-injection spark-ignition engines generally have low pumping losses.
Pumping losses comprise the energy required to intake air through an intake system, pump it through the engine, and out of an exhaust system. Pumping losses reduce the total amount of energy that the engine translates into work. A typical multi-cylinder engine has an engine block with multiple cylinders, and a piston in each cylinder that is operably attached to a crankshaft. There is also at least one intake valve and at least one exhaust valve that allow passage of air into and out of each cylinder. A combustion chamber is formed inside each cylinder. The typical engine operates on a four-stroke combustion cycle that sequentially includes an air intake stroke, a compression stroke, a power stroke, and an exhaust stroke. During the air intake stroke the piston moves away from the intake and exhaust valves and creates a negative pressure in the combustion chamber. Pumping loss during air intake is due to the negative pressure in the combustion chamber that is working against the movement of the piston away from the intake and exhaust valves. During the exhaust stroke the piston moves toward the intake and exhaust valves and creates a positive pressure in the combustion chamber. Pumping loss during exhaust is due to the positive pressure in the combustion chamber that is working against the movement of the piston toward the intake and exhaust valves.
When a cylinder is active, the pumping loss during air intake is a measure of a restriction in the air intake system and includes air flow restrictions between the combustion chamber and the outside air, i.e. the intake valves, the intake manifold, any throttle device, and an air cleaning device. The pumping loss during exhaust is a measure of a restriction in the exhaust system and includes airflow restrictions between the combustion chamber and the outside air, i.e. the exhaust valves, the exhaust manifold, exhaust pipes, mufflers, resonators, and any exhaust aftertreatment devices, including catalytic converters. On engines employing an air throttle device, pumping losses are greatest during periods of low engine power usage. This is due to a large airflow restriction, and corresponding negative pressure, into the combustion chamber when the throttle device is only partially opened. Internal combustion engines and pumping loss measurement and description is well known to one skilled in the art.
When one or more cylinders is deactivated, there is a reduced demand in the intake system for incoming air. The reduced demand for incoming air results in less negative pressure being created in each combustion chamber during the intake stroke. On engines employing an air throttle device, the effect of the reduced demand for incoming air is more pronounced, in terms of the effect of the restriction on airflow. This results in less pumping loss through the engine, resulting in higher translation of energy into power, or work.
One form of a cylinder deactivation system operates by collapsing the opening mechanisms of the intake and exhaust valves of each deactivated cylinder, so the deactivated intake and exhaust valves all remain in closed positions. Fuel delivery is also discontinued to each deactivated cylinder. This action stops the flow of air and fuel to each deactivated cylinder. When cylinder deactivation occurs, an engine controller may also increase the amount of fuel delivered to the active cylinders, to meet the extant power demands of the engine and vehicle. This results in higher temperatures in each active cylinder. The active cylinders each operate with greater airflow, reducing pumping losses due to throttling of the air intake, and improving thermal efficiency.
To improve the warm-up and interior heating of a vehicle with a compression-ignition engine, the prior art has added a valve in the exhaust system to inhibit the flow of excess air on engine start-up. While this approach does inhibit the flow of air into the engine, and improve warm-up rate, it also increases the pumping losses of the engine, which serves to significantly negatively affect fuel economy. The prior art has also added electric space heaters to the passenger compartment, with related problems of packaging, durability, safety, and electrical energy consumption.
The prior art has also sought to increase engine-operating temperature by changing engine operation. The combustion temperature of a compression ignition engine is increased by restricting airflow to the engine using a throttle device. The combustion temperature is also increased by increasing engine exhaust gas re-circulation (EGR), changing timing of engine fuel injection to the cylinder, or changing timing of opening or closing of intake and exhaust valves. Each of these approaches may increase exhaust gas temperature, but may also result in decreases in engine performance and fuel economy, and increases in exhaust emissions.
Hence, there is a need to be able to improve the engine warm-up rate and passenger compartment heating without affecting fuel economy, or increasing exhaust emissions. There is also a need to minimize added hardware to the engine, and to use existing hardware on the vehicle. This need exists especially for engines that operate primarily at an air/fuel ratio that is lean of stoichiometry, such as compression ignition and direct-injection spark ignition engines. The need to improve engine warmup rate also exists for high-efficiency spark-ignition engines.
The present invention is an improvement over conventional systems for heating of an internal combustion engine and a passenger compartment of a vehicle, in that it is able to employ cylinder deactivation hardware and an engine control system to increase the heat rejected to the engine cooling system. This is intended for use in engines that primarily operate at air/fuel ratios that are lean of stoichiometry. The present invention also includes reducing cooling system heat capacity on all engine systems, including both stoichiometric and non-stoichiometric engines. The heat rejected to the cooling system is a result of an increase in combustion temperatures in the non-deactivated cylinders, due to increased work and a reduction in airflow through the engine. The reduction in cooling system heat capacity is a result of separating coolant fluid flowing through the engine such that the coolant fluid flowing to the passenger compartment heating system only flows through the engine past the activated cylinders. The addition of extra heat to the cooling system, combined with a reduction in effective volume of the cooling system act together to reduce the amount of time necessary for the engine cooling system to reach a sufficient temperature to provide useful heat to a vehicle interior after a cold start. This action provides heat quickly after a cold start and while operating at low engine power operating points. This method and system are particularly suited to engines that primarily operate at an air/fuel ratio that is lean of stoichiometry, i.e. compression-ignition engines and direct-injection spark ignition engines. The system monitors coolant temperature and engine operating point, and deactivates at least one cylinder based upon the coolant temperature and the engine operating point. The system also increases the amount of fuel delivered to each of the non-deactivated cylinders by an amount sufficient to maintain the operating point of the engine. The cylinder deactivation system preferably includes decoupling an opening mechanism of each intake and exhaust valve, and disabling fuel delivery to the deactivated cylinder(s). These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.